Babies born with a larger head may have an increased risk of childhood brain cancer, research suggests.
Head circumference at birth reflects brain size, and researchers suspected that in some cases this might be a sign of abnormal growth patterns.
A Norwegian Institute of Public Health team tested their hypothesis by examining the health records of over a million young people.
They found the larger the head at birth, the greater the risk.
For every centimetre increase in head circumference at birth, the relative risk of having a tumour rose by 27%.
However, the overall risk was still small. Out of 1,010,366 children in the study just 453 were diagnosed with brain cancer.
In the UK, about 300 children are diagnosed with a brain tumour each year. Currently, around 30% of affected children die of the disease.
The researchers said their work suggested that brain cancers might begin to develop before birth.
Cancer cells - and particularly those that play a key role in developing blood supply to a tumour - are thought to be stimulated by the same growth factors as healthy tissues during development.
Thus if healthy tissues grow at a faster rate than usual, then maybe growth factors are present at levels that make the development of malignant tissues more likely too.
Another hypothesis is that large children may be more prone to cancer simply because they have more cells.
However, there was no significant association between head size and the risk of other cancers.
Lead researcher Dr Sven Ove Samuelsen said: "To our knowledge, this is the first study to report an association between increased head circumference at birth and brain cancer in childhood.
"Our findings suggest that brain pathology originates during foetal life in children diagnosed with brain cancer."
He said further research was needed to confirm the findings.
Professor John Toy, medical director of Cancer Research UK, said: "Brain cancer in children is very rare and we welcome any insight that helps us to understand it further.
"This study has used seemingly robust data and shown some very interesting results.
"However, the relationship between head circumference with statistical cancer risk is very complex.
"Many unanswered questions clearly remain and more work will be needed before any definite conclusions can be drawn.
"Hopefully this data will stimulate new research questions."
Previous research has linked exposure to x-rays in the womb with brain tumours. Other factors may include exposure to pesticides, solvents and animal viruses.